The typical carpenter's square has been well known for many years and is a very necessary and useful tool in most fields of construction. Hardly anyone, whether a professional carpenter or craftsman, or mere amateur do-it-yourself home builder, has ever done any woodworking without having had to employ a square at one time or another. The square is the only convenient tool for assuring that two pieces of material have been fitted together exactly perpendicularly to each other, or that a single piece of material has adjacent edges which meet at a right angle. As is well known in many forms of professional or home workshop construction, it is most critical that complementary pieces of material fit together at a right angle, or that individual pieces have adjacent edges which meet at a right angle, in order for the finished product to be properly constructed in terms of rigidity, strength and aesthetic appearance. Tight tolerances are the rule, rather than the exception when dealing with this kind of work.
Although the basic configuration of the carpenter's square has remained unchanged since the square was first developed, many improvements have been made which have substantially increased the efficient utilization of the square, as a result of which many different types of squares exist today. For example, the professional carpenter's square is still nothing more than a single piece of metal formed in the shape of an "L", that is, two legs joined to each other at a 90.degree. angle, each leg having markings thereon to indicate increments of linear measurement. Typically, the legs of this type of square are unequal and between 1 and 2 feet long since the square is used where the pieces of material have large dimensions, such as in the construction of a house. A smaller, more portable square, suitable for carrying on a tool belt and commonly known as a "speed square", is favored by many craftsmen.
It is well known that carpenter's and other skilled workmen prefer to carry and use a minimum number of tools. Since a carpenter's square is an essential tool, numerous attempts have been made to improve the tool, often by combining the square with other tools or by adding features to the square. U.S. Pat. No. 3,499,225 to Darrah, for example, provides a 2-piece hinged square with a horizontal level built into the tool. The tool includes a substantially V-shaped portion for fitting closely with a pipe or other member of circular cross-section, with magnets for attaching the tool to the pipe. The tool is designed primarily for ironworking, however, and does not address the recurring carpenter's problem of using a plumb bob to check corners which have been squared using the tool itself.
U.S. Pat. No. 3,826,013 to Baher combines level, square, and plumb functions in one tool. However, Baher achieves its plumb readings indirectly by reading a horizontal bubble level held on an arm at right angles to the surface being plumbed. Such a reading would be likely to produce inaccuracies over distances greater than a few feet, when compared to equivalent plumb readings obtained by use of a plumb bob. Various other inventions have combined levels with squares, either as a way to achieve a plumb reading, or simply to add a level function, or as a combination of both. U.S. Pat. No. 4,503,624 to Whiteford combines a level with a square, with the intent of achieving a plumb reading. However, Whiteford suffers from the same inaccuracy drawbacks as Baher. U.S. Pat. No. 5,253,426 to Mosbrucker is similar in concept to Whiteford and Baher, and suffers from the same inaccuracy drawback.
U.S. Pat. No. 5,269,066 to Walters illustrates an attempt to solve the accuracy problems of Whiteford, Baher, and Mosbrucker. Walters utilizes a square having full-length level bubbles contained in its legs. By combining full-length bubbles with long legs--the square of Walters' FIG. 1 is 16.times.24 inches--Walters is presumably able to provide much more accurate plumb readings. However the Walters square is not a convenient size for a carpenter to carry on his tool belt. Moreover, it is still not certain that the plumb readings of Walters would be as accurate as those obtained using a conventional plumb bob. A further attempt to solve the above-mentioned accuracy problems may be found in U.S. Pat. No. 5,239,761 to Wu, et al. Wu combines a square with an actual built-in plumb bob to allow for accurate plumb readings. However, the tool of Wu suffers from the drawback of not providing a no-hands means for fixing the plumb bob in place. Therefore, taking plumb bob readings remains a two-man job with the Wu tool. In an attempt to solve this problem, magnets have been used to free the hands of the user of various tools. For example, U.S. Pat. No. 4,593,475 to Mayes provides a level with magnetic support.
Despite all the attempts to improve on conventional squares by adding levels and plumb reading capabilities, there still remains a need for a convenient, highly portable tool which can accurately perform all the squaring, levelling, and plumb-reading functions which are repeatedly encountered in a variety of carpentry and other tasks. In addition, it would be ideal if such a tool were operable by a single workman. A tool which could accomplish the foregoing would take the place of several tools, and would allow a single workman to perform tasks which normally require at least two workmen to perform.